Multi-Wavelength Raman-Rayleigh Lidar for Atmospheric Remote Sensing
Document ID: 108
Doctoral Dissertation
The Pennsylvania State University
The Graduate School
Department of Electrical Engineering
Abstract
Several different lidar analysis techniques have been applied to the measurements of atmospheric properties, with particular emphasis on temperature profile from the ground to 80 km using the Penn State lidar instrument These different lidar techniques are the molecular scattering (Rayleigh) lidar with wavelength at 532 nm or 355 nm, the two-wavelength lidar using the combination of returns from wavelengths at 532 nm and 355 nm, and the molecular nitrogen scatter Raman lidar at a wavelength of 607 nm. In the upper stratosphere and mesosphere, from 30 km to 80 km, the single-wavelength molecular scatter lidar technique has proven successful and has been demonstrated to be preferable for measurements of atmospheric density and temperature using the molecular backscattered signal.
An important result from two-wavelength lidar is the ability to define the minimum height range that can be used for molecular scatter analysis. Further, the two-wavelength lidar technique has limited use for the stratospheric density and temperature measurements, this technique has been used to separate the molecular and particle portion of the backscattered signal in the upper region of the stratospheric volcanic aerosol layer, 27 km to about 35 km. By observing the twowavelength particle backscatter ratio, we monitored the presence of volcanic particles and concluded that there were usually two or more particle types in the stratospheric aerosol layer during the LADIMAS Campaign, October through December 1991.
The tropospheric density and temperature profiles have been determined from the transmission-corrected vibrational N2 Raman channel signal, under some atmospheric conditions. Density and temperature measurements, using the N2 Raman signal, were compared with the results of balloon measurements and generally good agreement was found from 1 km to 15 km, when the troposphere was cloudless. We found that the quality of the retrieved tropospheric density and temperature profiles, obtained above the boundary layer, depends upon there being no strong layers of clouds present. The tropospheric extinction profile has been derived from the vibrational Raman N2 signal by using the difference between the signal profile and a model or a balloon measured density profile. More recently, the rotational Raman technique has provided accurate tropospheric temperature measurements from the ground to 5 km, even in the presence of tropospheric aerosols and thin cloud layers.
This research effort has investigated the conditions of applicability of molecular scattering (Rayleigh) lidar, two-wavelength Rayleigh lidar, and vibrational Raman and rotational Raman lidar techniques. The two-wavelength lidar technique can identify regions containing aerosols, and show when the dominant aerosol type changes. We have demonstrated the limitations and potential capabilities of Rayleigh and Raman techniques. Vibrational and rotational components of the Raman scatter can be used for measurements of atmospheric structure properties and for definition of the optical environment.
| Citation: | Y. -C. Rau, "Multi-Wavelength Raman-Rayleigh Lidar for Atmospheric Remote Sensing", The Pennsylvania State University, Doctoral Dissertation, May 1994, 126 pages |